Applicants"" invention relates to charging a battery in a portable electronic apparatus, e.g., a mobile radio communication system such as a portable cellular telephone, a cordless phone, a pager, etc. The invention more particularly relates to methods and apparatus for delivering a constant current from a charger to a battery in a cellular phone using control logic in the phone.
Mobile communication technology has evolved from early analog systems, e.g., the NMT450 and NMT900 systems in Scandinavia, the AMPS system in the U.S., and the TACS and ETACS services in the United Kingdom, to more sophisticated digital systems, e.g., the Global System for Mobile Communications (GSM) in Europe and the American Digital Cellular System (ADC) in North America. Modern digital mobile communication systems are capable of voice transmission as well as other digital services, facsimile transmissions, and short message services.
Mobile communication devices like cellular phones should preferably be small, lightweight, and inexpensive, yet exhibit good battery performance and be capable of providing many services. The communication device should not have any unnecessary external connectors, which are expensive and increase the size and weight of the device. To ensure proper operation of a battery-powered communication device, it is critical that the battery is correctly charged (and discharged). Preferably, the communication device should be operable while the battery is charging, so that operation need not be repeatedly interrupted to recharge the battery.
Among the known techniques for charging a battery in a portable communication device is connecting a battery charger to the battery through the communication device. This may be done by placing a cellular phone in a click-in battery-charging holder in a car. A switch is often included that operates only to switch off the charging current when the battery is fully charged. Charge is delivered to the battery only when the cellular phone is placed in the click-in holder. Since charge is depleted during a call, the cellular phone must be put back in the click-holder to recharge the battery and interruption may result. Furthermore, these devices do not distinguish between different types of batteries, so that a cellular phone may be erroneously connected to an inappropriate charger, resulting in incorrect charging and possible damage to the battery.
To correct the problem of incorrect charging, U.S. Pat. Nos. 5,164,652 and 5,237,257, both to Johnson et al., disclose devices for determining the type of battery connected to the charger and adjusting charging parameters accordingly so that the battery is correctly charged. To prevent improperly discharging a battery, U.S. Pat. No. 5,177,426 to Nakanishi et al. discloses a device using circuitry in the charger to stop current from flowing from the battery to the phone. Such devices typically employ logic circuitry that is part of the charger, which increases the cost of the charger and the overall cost of the cellular system.
Other known battery-charging devices include xe2x80x9cintelligent batteriesxe2x80x9d that store information relating to battery condition, number of charges, and number of discharges in circuitry included in the battery pack. Also known are xe2x80x9cintelligent chargersxe2x80x9d that sense the condition of a connected battery and charge the battery accordingly.
Such devices are undesirable in portable cellular phones because they add components to the battery and charger that increase the overall cost and weight of the phone. It would be preferable to keep all necessary logic circuitry outside of the battery and charger, where it might be more cost effectively integrated with already existing circuitry.
Yet another device for charging a battery is disclosed in European Patent Publication No. EP 0 450 783 A2 by Martensson that shows control logic in a phone for controlling an external charger. In this device, there must be two-way communication between the phone and the external charger, which requires a control wire and results in a complicated battery charging process.
It is an object of Applicants"" invention to control the charging of a battery in a portable chargeable device, such as a cellular phone, by using simple control logic that is easily integrated with existing circuitry in the portable device.
It is another object of Applicants"" invention to prevent incorrect charging of a battery with an inappropriate battery charger.
It is another object of Applicants"" invention to keep the current level of a battery constant so that the battery is not overcharged, yet not to interrupt operation of the portable device to recharge the battery.
It is another object of Applicants"" invention to control the charging of a battery using circuitry in the portable device without requiring control circuitry in the battery charger or battery.
According to Applicants"" invention, a battery charger is capable of charging a battery in a portable device, such as a cellular radio telephone, with a long term constant current, even while the device is being used. Charging current is controlled by circuitry within the device, thus avoiding the need for control circuitry in the charger or battery.
According to one aspect of Applicants"" invention, a battery-charger connector is keyed to fit only a charger that corresponds to a type of battery in the portable device so that the battery is properly connected to an appropriate battery charger. According to another aspect of the invention, a simple contact is provided to connect a battery charger to the battery. A belt clip may be further provided to cover the battery-charger connector when the charger is not connected to the battery to prevent the battery from being short-circuited.